Climatic and geologic controls on suspended sediment flux in the Sutlej River Valley, western Himalaya

摘要

The sediment flux through Himalayan rivers directly impacts water quality andis important for sustaining agriculture as well as maintaining drinking-waterand hydropower generation. Despite the recent increase in demand for theseresources, little is known about the triggers and sources of extreme sedimentflux events, which lower water quality and account for extensive hydropowerreservoir filling and turbine abrasion. Here, we present a comprehensiveanalysis of the spatiotemporal trends in suspended sediment flux based ondaily data during the past decade (2001–2009) from four sites along theSutlej River and from four of its main tributaries. In conjunction withsatellite data depicting rainfall and snow cover, air temperature andearthquake records, and field observations, we infer climatic and geologiccontrols of peak suspended sediment concentration (SSC) events. Our studyidentifies three key findings: First, peak SSC events (≥ 99th SSCpercentile) coincide frequently (57–80%) with heavy rainstorms andaccount for about 30% of the suspended sediment flux in the semi-arid toarid interior of the orogen. Second, we observe an increase of suspendedsediment flux from the Tibetan Plateau to the Himalayan Front at mean annualtimescales. This sediment-flux gradient suggests that averaged, modernerosion in the western Himalaya is most pronounced at frontal regions, whichare characterized by high monsoonal rainfall and thick soil cover. Third, inseven of eight catchments, we find an anticlockwise hysteresis loop of annualsediment flux variations with respect to river discharge, which appears to berelated to enhanced glacial sediment evacuation during late summer. Ouranalysis emphasizes the importance of unconsolidated sediments in thehigh-elevation sector that can easily be mobilized by hydrometeorologicalevents and higher glacial-meltwater contributions. In future climate changescenarios, including continuous glacial retreat and more frequent monsoonalrainstorms across the Himalaya, we expect an increase in peak SSC events,which will decrease the water quality and impact hydropower generation.